1. Field of the Invention
The present invention relates to a resolution test device and a method thereof, and more particularly, to a test device and a method for testing the short-distance resolution of a camera device.
2. Description of Related Art
At present, the short-distance resolution of a camera needs to be tested during manufacture process. In a typical test method, contrast transfer function chart (CTF chart) is generally used to calculate the resolution. A to-be-calculated small area on an image outputted by a sensor is selected to calculate the lens resolution. However, this type of test brings errors due to positions of the camera or fixture or assembly of the sensor.
As to the selection of frequency of the CTF chart, if the frequency of the CTF chart is too low, i.e. the width of the black bar and the white bar is too large, the calculation will have inadequate accuracy. For example, in FIG. 1, seven black bars are in a dotted line framed area 110. After shifted, the solid line framed area 120 frames eight black bars. The high-pass elements of these two areas are different, and the corresponding resolutions are also different, thus causing instability of the test. In addition, in the contrast value test results of FIG. 2, multiple numbers of the movement steps of a focusing lens correspond to the same contrast value, i.e. the low frequency CTF chart may also cause the test inaccuracy as in FIG. 2. A CTF pattern with higher frequency is usually used to overcome this problem. However, the high frequency CTF pattern also makes it difficult to achieve uniform calibration of the fixtures along the product line and also difficult to fabricate the fixtures, thus resulting in a high cost. As a result, the product line often lacks of a good and uniform test system for testing the short-distance resolution of the lens.